Titanium oxide for incorporation into thermoplastic resin composition, thermoplastic resin composition, and molded object thereof

ABSTRACT

A thermoplastic resin composition which comprises (A) 40 to 98 mass % thermoplastic resin and (B) 60 to 2 mass % titanium oxide particles whose surface has been coated with a hydrous oxide and/or oxide of at least one metal selected from the group consisting of aluminum, silicon, zirconium, tin, cerium, titanium, and zinc, wherein the titanium oxide particles contain 80 to 97 mass %, excluding 97 mass %, titanium oxide ingredient and have total content of alkali metal cations and alkaline earth metal cations extractable with pure water of 120 mass ppm or lower. The resin composition is excellent in reflectance and thermal stability in residence during molding into large products.

TECHNICAL FIELD

The present invention relates to a thermoplastic resin composition suchas a polycarbonate resin composition and a molded object thereof, andmore particularly, to a thermoplastic resin composition having highreflectance and excellent thermal stability in residence such as apolycarbonate resin composition, and a molded object thereof.

BACKGROUND ART

Because of excellent in properties such as mechanical strength(especially, impact-resistant properties), electrical properties,transparency etc., polycarbonate resins have been widely used asengineering plastics in various sectors such as office automationequipment, electrical and electronic equipment, automobiles, etc.Recently, in the field of liquid-crystal displays, high reflectancematerials made of polycarbonate resins increasingly have greater use inbacklight application. Among others, application to monitors andtelevisions is remarkable, and enlargement of a backlight member isincreasingly in progress as the display size is becoming larger.Accordingly, as parts of the backlight member such as a reflectingplate, a reflecting frame, a cold cathode-ray tube supporter etc. arebecoming lager and the residence time during molding is becoming longer,there is a tendency that thermal stability in residence under hardermolding conditions than with conventional conditions is desired. Inaddition, since manufacturing abroad has become frequent due toglobalization in recent years, a material having a wide range ofmanufacturing conditions is increasingly desired, wherein the materialcan provide good products regardless of the level of skills or the levelof perfection of molding techniques or molding machines.

On the other hand, in order to provide a reflecting function,incorporation of titanium oxide into polycarbonate-type resins orpolyester-type resins has been conventionally performed. In such a case,methods for improving the thermal stability in residence have beengenerally adopted, for example, to prevent hydrolysis reaction betweenthe polycarbonate resins and titanium oxide by using a method such ascoating titanium oxide with a reactive silicone in advance. However,there was a problem, that is, when the amount of titanium oxide wasincreased in order to improve the reflectance of the composition, thethermal stability in residence during molding became increasingly poor,resulting in the reduction of the reflectance and appearance of themolded object, and hence it was generally difficult to make highreflectance and the thermal stability in residence during moldingcompatible with each other.

Further, there is disclosed a resin composition wherein an inorganicfiller whose base amount is 20 μmole/g or less is used in order toprovide a resin with sufficient thermal decoloration resistance andmechanical strength (refer to, for example, Japanese UnexaminedPublication No. H9-3211, page 1 to page 4). In order to improve thereflectance by blending titanium oxide, it is preferable to increase thecoating amount of a hydrous oxide and/or an oxide of a metal, forexample, silica-alumina on the surface of titanium oxide particles (thebase amount becomes 20 μmole/g or more). However, when commerciallyavailable titanium oxide particles with a large coating amount ofsilica-alumina were used directly, there was a phenomenon of lowering ofthe thermal stability in residence, that is, there was a limit in theimprovement of thermal stability in residence by using only the methoddescribed above, wherein the titanium oxide was coated with a reactivesilicone in advance.

DISCLOSURE OF THE INVENTION

The present invention was made in view of the situation, and an objectof the present invention is to provide a thermoplastic resincomposition, such as a polycarbonate resin composition, etc., whereinthe thermoplastic resin composition has excellent reflectance andthermal stability in residence during molding into large products.

The present inventors have studied intensively to solve the problemdescribed above and have found that a thermoplastic resin compositionand a molded object thereof satisfy the object, wherein a thermoplasticresin and titanium oxide coated with a hydrous oxide and/or an oxide ofat least one metal selected from the group consisting of aluminum,silicon, zirconium, tin, cerium, titanium and zinc are blended each in aspecified amount, and completed the present invention.

That is, the present invention provides a thermoplastic resincomposition which comprises (A) 40 to 98 mass % of a thermoplastic resinand (B) 60 to 2 mass % of titanium oxide particles coated with a hydrousoxide and/or an oxide of at least one metal selected from the groupconsisting of aluminum, silicon, zirconium, tin, cerium, titanium andzinc, wherein the titanium oxide particles contain 80 to 97 mass %,excluding 97 mass %, of titanium oxide ingredient and the total amountof alkali metal cations and alkaline-earth metal cations dissolved intopure water is 120 mass ppm or less, and a molded object thereof.

THE MOST PREFERRED EMBODIMENT TO CARRY OUT THE INVENTION

In the thermoplastic resin composition of the present invention, as thethermoplastic resin used as ingredient (A), it is preferable to use acolorless transparent resin such as a polycarbonate-type resin, anacrylic-type resin such as polymethyl methacrylate (PMMA) and the like,a polyester-type resin such as polyethylene terephthalate (PET),polybutylene terephthalate (PBT) and the like, a styrene-type resin, apolyether-nitrile resin (PEN), a liquid-crystal resin (LCP), etc. Theseresins may be used alone or in a combination of two or more thereof.When, as the thermoplastic resin to be used, the polycarbonate-typeresin, the polyester-type resin and the liquid-crystal resin that havecarbonate bonding or ester bonding in their molecular skeletons andhence have a problem of hydrolysis reaction are used, substantial effectof the thermal stability in residence is obtained. Among these resins,it is preferable to use the polycarbonate-type resin alone or thethermoplastic resin in which the amount of the polycarbonate-type resinis 50 mass % or more , also from the point of maintaining the mechanicalstrength.

As the polycarbonate resin, various resins can be named, however, apolymer having a repeated unit of the structure represented by generalformula (I) is preferable.

In the above general formula (I), X¹ and X² independently refer to alinear-chain, branched, or cyclic alkyl group with 1 to 8 carbon atoms,and specific examples include methyl group, ethyl group, n-propyl group,isopropyl group, n-butyl group, isobutyl group, tert-butyl group, n-amylgroup, isoamyl group, n-hexyl group, isohexyl group, cyclopentyl group,cyclohexyl group, and the like. The X¹ and X² may be identical ordifferent. The symbols a and b refer to the number of substitutions ofX¹ and X², respectively, and the number ranges from 0 to 4. If there isa plurality of X¹s, the X¹s may be identical or different, and if thereis a plurality of X²s, the X²s may be identical or different each other.

Y indicates single-bond, alkylene group having 1 to 8 carbon atoms (forexample, methylene group, ethylene group, propylene group, butylenegroup, pentylene group, hexylene group, etc.), alkylidene group having 2to 8 carbon atoms (for example, ethylidene group, isopropylidene group,etc.), cycloalkylene group having 5 to 15 carbon atoms (for example,cyclopentylene group, cyclohexylene group, etc.), cycloalkylidene grouphaving 5 to 15 carbon atoms (for example, cyclopentylidene group,cyclohexylidene group, etc.), —S— bond, —SO— bond, —SO₂— bond, —O— bond,—CO— bond, or a bond represented by formulas (II-1) or (II-2).

In general, the polymer described above can be easily manufactured byreacting a divalent phenol represented by general formula (III)

(wherein X¹, X², a, b and Y are the same as defined above.) and acarbonate precursor such as phosgene, a carbonate ester compound, or thelike.

That is, the above polymer may be manufactured, for example, by reactinga divalent phenol and a carbonate precursor such as phosgene in asolvent such as methylene chloride in the presence of a known acidreceptor or a molecular weight regulating agent, or by an ester-exchangereaction of a divalent phenol and a carbonate precursor such as acarbonate ester compound in the presence or absence of a solvent.

As the divalent phenol represented by the general formula (III)described above, various phenols can be named, however,2,2-bis(4-hydroxyphenyl)propane (so-called bisphenol A) is particularlypreferable. The divalent phenols other than bisphenol A can beexemplified by the following: bis(4-hydroxyphenyl) alkanes such asbis(4-hydroxyphenyl)methane, 1,1-bis(4-hydroxyphenyl)ethane,1,2-bis(4-hydroxyphenyl)ethane and the like,bis(4-hydroxyphenyl)cycloalkanes such as1,1-bis(4-hydroxyphenyl)cyclohexane, 1,1-bis(4-hydroxyphenyl)cyclodecaneand the like, 4,4′-dihydroxydiphenyl, bis(4-hydroxyphenyl)oxide,bis(4-hydroxyphenyl)sulfide, bis(4-hydroxyphenyl)sulfone,bis(4-hydroxyphenyl)sulfoxide, bis(4-hydroxyphenyl)ether,bis(4-hydroxyphenyl)ketone, etc. In addition, as the divalent phenols,examples include hydroquinone, etc. These divalent phenols may be usedalone or in a combination of two or more thereof.

As the carbonate ester, for example, diaryl carbonates such asdiphenylcarbonate, dialkyl carbonates such as dimethylcarbonate,diethylcarbonate, etc., can be named.

When a polycarbonate is manufactured by reacting the divalent phenol andthe carbonate precursor described above, a molecular weight regulatingagent may be used as required. The molecular weight regulating agent isnot specifically limited, and an agent which has been conventionallyused in polycarbonate manufacturing may be used. As a such agent, forexample, monovalent phenols such as phenol, p-cresol,p-tert-butylphenol, p-tert-octylphenol, p-cumylphenol, nonylphenol andthe like can be named.

The polycarbonate resin may be a homopolymer of one of the divalentphenols or a copolymer of two or more of the divalent phenols describedabove. Further, the polycarbonate resin may be a thermoplastic randombranched polycarbonate resin obtained by a combination of apolyfunctional aromatic compound and the monovalent phenol describedabove.

Also, the polycarbonate resin may be a polycarbonate-polyorganosiloxanecopolymer comprising an organosiloxane block having the number averagedegree of polymerization of 5 or more.

Further, the polycarbonate resin may be a mixture of two or more ofvarious polycarbonate resins.

As the polycarbonate resin used as ingredient (A) in the composition ofthe present invention, a polycarbonate resin having theviscosity-average molecular weight (Mv) in the range of 13,000 to30,000, and in particular 15,000 to 25,000 is preferable, from the pointof mechanical strength, especially such as Izod impact strength,moldability, etc.

Polycarbonate resins having such properties are commercially availableas aromatic polycarbonate resins, for example, such as Tarflon FN3000A,FN2500A, FN2200A, FN1900A and FN1500A (trade names, made by IdemitsuPetrochemical Co., Ltd.).

In the thermoplastic resin composition of the present invention, theblending ratio of the thermoplastic resin is from 40 to 98 mass %, andpreferably from 70 to 95 mass %. If the blending ratio of thethermoplastic resin is less than 40 mass %, the blending ratio oftitanium oxide that is an inorganic substance becomes too large, so thatmolding becomes difficult, or mechanical properties such as impactstrength decreases. If the blending ratio is more than 98 mass %, theamount of titanium oxide particles used as ingredient (B) becomes toosmall, and reflectance of a molded object obtained is not improved.

The blending ratio of the titanium oxide particles as ingredient (B) isfrom 60 to 2 mass %, and preferably from 30 to 5 mass %. If the blendingratio of the titanium oxide particles is less than 2 mass %, reflectanceof the molded object obtained is not improved. If the blending ratio ofthe titanium oxide particles is more than 60 mass %, molding becomesdifficult, or mechanical properties such as impact strength decreases.

The titanium oxide particles as ingredient (B) are particles wherein thesurface of titanium oxide is coated with a hydrous oxide and/or an oxideof at least one metal selected from the group consisting of aluminum,silicon, zirconium, tin, cerium, titanium and zinc. As the titaniumoxide particles as ingredient (B), those containing titanium oxideparticles having 80 to 97 mass %, excluding 97 mass % are used. If theamount of titanium oxide ingredient is 97 mass % or more, the amount ofthe metal hydrous oxide and/or the metal oxide of the surface coatinglayer becomes small, and reflectance of the obtained molded object isnot improved. Also, if the amount of titanium oxide ingredient is lessthan 80 mass %, the amount of the metal hydrous oxide and/or the metaloxide on the particle surface becomes too large and the coating layerbecomes too thick, which is not preferable because of the followingreasoning: The too thick coating layer leads to a significant increasein the equilibrium water absorption coefficient (the water amount at 25°C. and the humidity of 55% in 2 hours) and consequently to a value over0.5 mass %, and may cause hydrolysis of the thermoplastic resin such aspolycarbonate, etc. Accordingly, the amount of titanium oxide ingredientis preferably about 95 to about 90 mass %. Also, the particle size ofthe titanium oxide particles is generally about 0.1 to about 0.5 μm. Asthe titanium oxide powder, both of a rutile type and an anatase type canbe used, however, from the point of thermal stability, weatherability orthe like, the rutile type is preferable.

As the metal element of the metal hydrous oxide and/or the metal oxideof the surface coating layer, at least one element selected fromaluminum, silicon, zirconium, tin, cerium, titanium and zinc can benamed. In general, titanium oxide coated with silica and/or alumina ismost frequently used and is useful from the point of performance andcost.

Usually, titanium oxide particles coated with a metal hydrous oxideand/or a metal oxide described above and washed with water arecommercially available. However, probably because the washing level isnot high, alkali metals and alkaline-earth metals generated secondarilyduring a coating step remain, and alkali metal cations and/oralkaline-earth metal cations (hereinafter, may be called as metalcations) that are mainly originated from Na and K are attached to thesurface etc. of the titanium oxide particles. For example, the surfaceof titanium oxide is coated with silica and/or alumina by neutralizationof sodium silicate and/or sodium aluminate with an acid, for example.When sulfuric acid is used as the acid, sodium sulfate remains as abyproduct salt. If hydrochloric acid is used instead of sulfuric acid,sodium chloride will remain. As the acid, sulfuric acid, hydrochloricacid, nitric acid, phosphoric acid, acetic acid, oxalic acid and thelike can be named. However, sulfuric acid is preferable in terms ofcost, and phosphoric acid, acetic acid and oxalic acid are preferable interms of product performance from the point of dissociation constants ofresidual salts. Titanium oxide particles used in the present inventionshould have 120 mass ppm or less of the sum of metal cations (from Li,Na, K, Mg, and Ca) that are extracted to pure water as determined by ionchromatography analysis. If the total amount of the metal cationsextracted to pure water is more than 120 mass ppm, thermal stability inresidence during molding of the composition lowers substantially,wherein the thermoplastic resin (especially polycarbonate) and titaniumoxide particles are the main ingredients. The total amount of metalcations extracted to pure water is preferably 70 mass ppm or less, andin particular preferably 40 mass ppm or less.

Further, it is preferable that, when the total amount of alkali metalcations and alkaline-earth metal cations extracted to pure water isdesignated as X (mass ppm), the value of [the blending ratio of titaniumoxide powder (mass %)/the blending ratio of thermoplastic resin (mass.%)]×[X (mass ppm)] is 15 mass ppm or less. By making this value 15 massppm or less, thermal stability in residence during molding can beimproved.

In addition, as the guideline of the acceptable total amount of metalcations (mass ppm) in the titanium oxide extracted to water based on theblending ratio (mass %) of the titanium oxide particles, it ispreferable that the total amount is 120 mass ppm or less when theblending ratio of titanium oxide particles is 10 mass %, the totalamount is 90 mass ppm or less when the blending ratio of titanium oxideparticles is 15 mass %, the total amount is 60 mass ppm or less when theblending ratio of titanium oxide particles is 20 mass %, the totalamount is 35 mass ppm or less when the blending ratio of titanium oxideparticles is 30 mass %, and the total amount is 23 mass ppm or less whenthe blending ratio of titanium oxide particles is 40 mass %. If thetotal amount is more than the acceptable value, thermal stability inresidence decreases.

In the thermoplastic resin composition or the molded object thereof ofthe present invention, the sum of metal cations (from Li, Na, K, Mg, Ca)extracted to pure water as determined by ion chromatography analysis ispreferably 3 mass ppm or less based on titanium oxide. If the totalamount of the water-extractable metal cations from the thermoplasticresin composition is more than 3 mass ppm, thermal stability inresidence of the molded object during molding of the compositiondecreases substantially, wherein the composition comprises thermoplasticresin (especially polycarbonate) and titanium oxide particles as themain ingredients. Additionally, by making the total amount of thewater-extractable metal cations from the molded object 3 mass ppm orless, thermal stability in residence is improved. The total amount ofthe water-extractable metal cations from the thermoplastic resincomposition or molded object thereof is more preferably 2 mass ppm orless, further more preferably 1 mass ppm or less.

When the thermoplastic resin as ingredient (A) is a polycarbonate typeresin or a mixture of a polycarbonate type resin and anotherthermoplastic resin, depending on the blending ratio of titanium oxideparticles, it is preferable to blend 0.05 to 3 parts by weight oforganopolysiloxane as ingredient (C) to a total of 100 parts by weightof the thermoplastic resin as ingredient (A) and titanium oxideparticles as ingredient (B) in order to prevent decomposition of thepolycarbonate type resin. If the blending ratio of theorganopolysiloxane is less than 0.05 mass %, the polycarbonate resin maydegrade, and its molecular weight may decrease. Also, if the blendingratio of the organopolysiloxane is more than 3 mass %, a silver streakmay occur on the surface of the molded object and appearance of theproduct may become poor.

As the organopolysiloxane, alkyl hydrogen silicones, alkoxy siliconesand the like are named, for example, SH1107, SR2402, BY16-160, BY16-161,BY16-160E, and BY16-161E (made by Dow Corning Toray Co., Ltd.) can beused preferably.

In the thermoplastic resin composition of the present invention, a flameretardant as ingredient (D) may be blended, and in particular, it ispreferable to blend 0 to 7 mass % of a phosphorous-based flame retardantto a total of 100 mass % of the thermoplastic resin as ingredient (A)and titanium oxide particles as ingredient (B). As the phosphorous-basedflame retardant, a phosphate ester compound is named. The phosphateester compound has functions to stabilize thermal moldability of thethermoplastic resin composition as well as to provide excellent flameretardancy through a synergetic effect with titanium oxide in ingredient(B). As the phosphate ester compound, a halogen-free phosphate estercompound which does not contain halogen atoms such as bromine ispreferable, since a molded object containing it may cause lessenvironmental pollution when it is subjected to disposal treatment.

As the halogen-free phosphate ester compound, for example, phosphatemonoesters, phosphate ester oligomers, or phosphate polyestersrepresented by general formula (IV) can be named.

In the general formula (IV) described above, R¹ to R⁴, independently,refers to aryl group which may optionally have a substituent, and may beidentical or different. X refers to arylene group which may optionallyhave a substituent; c, d, e and f independently refers to 0 or 1; and prefers to a number from 0 to 5. When two kinds or more of phospateesters are used, the p is represented as the average value of each p ofthe phosphate esters. As the substituent in the aryl group and thearylene group described above, for example, alkyl group having 1 to 10carbon atoms, alkoxy group having 1 to 10 carbon atoms, and aryl groupsuch as phenyl group, tolyl group and the like can be named. Thesesubstituents may be introduced as a single substituent or a plurality ofsubstituents.

As the halogen-free phosphate ester compound represented by the generalformula (IV), phosphate monoesters such as triphenyl phosphate,tricresyl phosphate, trixylenyl phosphate, tribiphenyl phosphate and thelike, phosphorate ester oligomers thereof, or polyphosphate esters suchas phenylresorcine polyphosphate, phenylhydroquinone polyphosphate,phenylcresylresorcine polyphosphate, phenylcresylhydroquinonepolyphosphate, tetraphenylresorcine diphosphate, tetraphenylhydroquinonediphosphate, phenyltricresylresorcine diphosphate,phenyltricresylhydroquinone diphosphate, tetrabiphenylresorcinediphosphate, tetrabiphenylhydroquinone diphosphate, etc. can be named.Among them, phosphate ester oligomers and polyphosphate esters arepreferable from the point of reducing adhesion to a mold during thermalmolding of the polycarbonate resin composition. These phosphatemonoesters, phosphate ester oligomers and phosphate polyesters may beused singly or in a combination of two or more thereof.

In the composition of the present invention, the phosphate estercompound as ingredient (D) contains 0.05 to 1.00 mass % as thephosphorus element based on the total weight of the thermoplastic resinas ingredient (A) and titanium oxide particles as ingredient (B). If thephosphorus element amount is less than 0.05 mass %, the improving effecton the flame retardancy and the synergetic effect with titanium oxidemay not be shown sufficiently. Also, if the phosphorus element amount ismore than 1.00 mass %, improvement of the effects described above is notso large as expected, and this is rather economically unfavorable, andfurther thermal stability of the molded object tends to become poor.From the point of the improving effect on flame retardancy, thermalstability of the molded object, cost etc., an especially preferableamount of the phosphorus element is 0.1 to 0.5 mass % based on the totalweight of ingredient (A) and ingredient (B).

By adding a fluorinated resin as ingredient (E), the thermoplastic resincomposition of the present invention can gain further higher flameretardancy. The blending ratio of the fluorinated resin is preferably 0to 1.0 parts by weight based on the sum of (A) thermoplastic resin and(B) titanium oxide particles of 100 parts by weight. As the fluorinatedresin, a fibril-forming polytetrafluoroethylene with an averagemolecular weight of 500,000 or more is preferable. The fibril-formingpolytetrafluoroethylene can perform as a dripping inhibitor (aninhibitor of dripping of an ignited resin).

Here, the fibril-forming ability refers to an ability of a resin toundergo fibrillation when the resin is subjected to plastic shear stressin kneading or injection molding, and is effective in obtaining highflame retardancy.

Such a fibril-forming polytetrafluoroethylene (PTFE) described above canbe obtained by, for example, polymerizing tetrafluoroethylene in anaqueous solvent, in the presence of sodium-, potassium-, orammonium-oxydisufide, under the pressure of about 1 to about 100 psi,and at about 0 to about 200° C., preferably at 20 to 100° C.

There is no particular restriction in the type of thus obtainedfibril-forming PTFE. However, the type, for example, classified in Class3 in ASTM standards is suitable. As a practical commercial product,Teflon (registered trade mark) 6-J (trade name, made by DuPont MitsuiFluorochemical Co., Ltd.), Polyflon TFE D-1, Polyflon TFE F-104 (tradenames, made by Daikin industries, Ltd.), and the like are named. Otherthan those classified in Class 3, for example, Algoflon F5 (trade name,made by Montefluos Corp.), Polyflon MPA FA-100 and Polyflon TFE F201(trade names, made by Daikin industries, Ltd.), and the like are named.

The fibril-forming polytetrafluoroethylene as ingredient (E) may be usedsingly or in a combination of two or more thereof.

In the composition of the present invention, there is no particularrestriction in the amount of optionally used fibril-formingpolytetrafluoroethylene as ingredient (E). However, the range of 0.01 to1 mass % based on the total weight of the thermoplastic resin asingredient (A) and titanium oxide particles as ingredient (B) isadvantageous. If the amount is less than 0.01 mass %, its drippinginhibition effect may not be shown sufficiently. On the other hand, ifthe amount is more than 1 mass %, improvement of the effectcorresponding to the amount may not be obtained, and it may ratherbecome economically unfavorable.

The thermoplastic resin composition of the present invention mayappropriately contain, within the range where the object of the presentinvention is not damaged, if necessary, various additives, for example,an oxidation inhibitor, a lubricant (a mold releasing agent), anotherinorganic filler, or the like.

The thermoplastic resin composition of the present invention can beprepared by, for example, kneading after blending ingredient (A), andingredient (B); optionally used ingredient (C), ingredient (D), andingredient (E); and various additives. As the blending method and thekneading method, those applied to ordinary resin compositions can bedirectly used, and a method using ribbon blender, Henschel mixer,Banbury mixer, drum tumbler, single-axis screw extruder or multi-axisscrew extruder having two axes or more, cokneader, and the like ispreferable. In addition, there is no particular restriction in thekneading temperature, however, in general, the temperature isappropriately selected in the range of 240 to 340° C.

The resin composition obtained in this way is molded into a flat plateor a curved plate by using an ordinary molding method, for example,injection molding, compression molding or the like, and the moldedobject of the present invention is obtained. The molded object ispreferably used, for example, for lighting equipment and for backlightof a liquid-crystal display, and is especially preferable for abacklight reflecting plate of a liquid-crystal display.

Because of the absence of a bromine compound in its materials, themolded object of the present invention has excellent properties, such asexcellent lightfastness, small lowering of reflectance in a longduration, excellent characteristics, etc., that were not availablepreviously.

The present invention will be described in more detail with reference toexamples, however, the present invention is not to be construed as beinglimited thereto. In addition, the amount of the metal cations wasmeasured as follows.

(1) The Case of Titanium Oxide Particles

A 1 g aliquot of a sample was weighed into a 50 to 100 mL polyethylenecontainer inside of which was washed with pure water in advance, and wassuspended in 40 mL of pure water. A 1 g aliquot of the sample was dippedin 2 mL of methanol, suspended in water by adding 38 mL of pure water,shaken for one hour at room temperature, left standing for 30 minutesand precipitated. Next, after aspirating the supernatant with a syringe,the supernatant was passed through a disposable syringe filter having apore size of 0.45 μm (Chromatodisc, made by G L Science Corp.), anddirectly injected into an ion chromatography apparatus (DX-120, made byDIONEX Corp.) set with the following conditions and analyzed.

(2) The Case of the Composition (in Pellet) or the Molded Object

After dissolving 10 g of a pellet or a molded object containing titaniumoxide particles in 100 mL of methylene chloride, 40 mL of pure water wasadded to the methylene chloride solution. The resultant solution wasshaken for one hour and left standing to separate into an aqueous phaseand a methylene chloride phase. After aspirating the aqueous phaseextract with a syringe, the extract was passed through a disposablesyringe filter having a pore size of 0.45 μm (Chromatodisc, made by G LScience Corp.), and directly injected into an ion chromatographyapparatus (DX-120, made by DIONEX Corp.) set with the followingconditions and analyzed.

(3) The Analytical Conditions of the Ion Chromatography Apparatus

(Analytical Conditions for Cations)

Column: IonPac CG12A+IonPac CS12A

Eluent: 20 mmole/L of methane sulfonic acid

Flow rate: 1 mL/min

Suppressor: CSRS 4 mm in the recycle-mode

Detector: electric conductivity type

Sample injection volume: 100 μL

(Analytical Conditions for Anions)

Column: IonPac AG12A+IonPac AS12A

Eluent: 2.7 mmole/L of Na₂CO₃/0.3 mmole/L of NaHCO₃

Suppressor: ASRS 4 mm in the recycle-mode

Detector: electric conductivity type

Sample injection volumte: 100 μL

EXAMPLES Examples 1-8

(1) Preparation of Titanium Oxide Particles

Five kinds of commercial titanium oxide particles (PF-726, CR-90, CR-85,PC-3 and CR-63, made by Ishihara Sangyo Kaisha, Ltd.) were provided.PF-726 is the titanium oxide particles of which surface is coated withsilica-alumina (5 to 6 mass % in total), CR-90 is the titanium oxideparticles of which surface is coated with silica-alumina (10 mass % intotal), CR-85 is the titanium oxide particles of which surface is coatedwith silica-alumina (12 mass % in total), PC-3 is the PF-726 describedabove coated with a polysiloxane, and CR-63 is the titanium oxideparticles of which surface is coated with silica-alumina (2.5 mass % intotal).

The total amount of metal cations of each of these commercial titaniumoxides was measured with ion chromatography analysis. As the result, thetotal amount of metal cations was confirmed to be 124 mass ppm inPF-726, 146 mass ppm in CR-90, 214 mass ppm in CR-85, 135 mass ppm inPC-3, and 40 mass ppm in CR-63. Incidentally, a substantial portion ofthese metal cations was sodium ion. Next, four kinds of the commercialtitanium oxide particles, excluding CR-63, were treated with a cleaningoperation described below, and water-washed products were obtained.

First, slurry containing 10 mass. % of titanium oxide particles wasprepared with pure water. Then, pH of the slurry was adjusted to 5.5 byadding an aqueous hydrochloric acid solution and the slurry was stirredfor one hour. After water-soluble ingredients were extracted, thesupernatant was removed. After adding pure water to the precipitatedtitanium oxide, the precipitate was aspirated, filtrated, and cleaned.The same filtrating and cleaning operations were repeated five times.After drying the obtained cake with a hot air dryer, the cake wassubjected to crushing treatment with a cutter mixer (K55, made byFujimac Corporation) at a rotating speed of 3,000 rpm two times.Further, the crushed cake was milled with a mortar to obtain thetitanium oxide powder.

The total amount of metal cations of the obtained water-washed titaniumoxide powder was measured with ion chromatography analysis. As theresult, the total amount of the metal cations was confirmed to be 20mass ppm in PF-726, 50 mass ppm in CR-90, 60 mass ppm in CR-85comprises, and 90 mass ppm in PC-3. These results are shown in Table 1.

TABLE 1 1 2 3 4 5 Kind of titanium oxide particles Commercial CommercialCommercial Commercial Commercial titanium oxide titanium oxide titaniumoxide titanium oxide titanium oxide PF-726 CR-90 CR-85 PC-3 CR-63 TiO₂amount (% by weight) 94 90 88 93 97.5 Total amounts of metal cations 124146 214 135 40 (weight ppm) before water-washing *1) Each amounts ofmetal Li 1 1 1 1 1 cation Na 120 142 210 128 33 (weight ppm) before K 11 1 2 2 water-washing *1) Mg 1 1 1 1 1 Ca 1 1 1 3 3 Total amounts ofmetal cations 20 50 60 90 — (weight ppm) after water-washing *2) Eachamounts of metal Li 1 1 1 1 — cation (weight ppm) after Na 16 46 56 86 —water-washing *2) K 1 1 1 1 — Mg 1 1 1 1 — Ca 1 1 1 1 — *1) Analyzedvalues of commercial titanium oxide powder *2) Analyzed values of purewater-washed product(2) Manufacturing of Thermoplastic Resin Compositions

The raw materials used are as follows.

-   -   (a) Polycarbonate-polydimethylsiloxane copolymer (PC-PDMS):        Tarflon FC1700 (Mv=18,000, PDMS amount; 3.5 mass %, made by        Idemitsu Petrochemical Co., Ltd.)    -   (b) Polycarbonate resin (PC): Tarflon FN1700A (Mv=18,000, made        by Idemitsu Petrochemical Co., Ltd.)    -   (c) Polymethyl methacrylate resin (PMMA): Sumipex MHF (made by        Sumitomo Chemical Co., Ltd.)    -   (d) Polybutylene terephthalate (PBT): TUFPET N100U (made by        Mitsubishi Rayon Co., Ltd.)    -   (e) Halogen-free phosphate ester (phosphorus-type flame        retardant): Adeka Stab PFR (phenylresorcine polyphosphate,        phosphorus amount; 10.8 mass %, made by Asahi Denka Co., Ltd.)    -   (f) Polytetrafluoroethylene (PTFE): Algoflon F5 (with        fibril-forming ability, molecular weight of 2,000,000 to        3,000,000, made by Montefluos Corp.)    -   (g) Organopolysiloxane: SH1107 and BY 16-161 (viscosity: 24        mm²/s and 27 mm²/s, respectively, made by Dow Corning Toray Co.,        Ltd.)

According to the blending ratio shown in Table 2, the polycarbonateresin, the polycarbonate-polydimethylsiloxane copolymer (PC-PDMS), otherthermoplastic resins, cleaned titanium oxide (water-washed product), theorganopolysiloxane, PTFE, and optionally the phosphorus-type flameretardant were blended, kneaded with a vented double-axis extruder(TEM-35B, made by Toshiba Machine Co., Ltd.) at 280° C., and pellets ofthe thermoplastic resin composition were made.

Each pellet was dried with hot air at 120° C. for 5 hours, and moldedinto a flat plate having the geometry of 140 mm×140 mm×3.2 mm forreflectance measurement by using a molding machine (Sumitomo-NestalN515/150, made by Sumitomo Heavy Industries, Ltd.) under the conditionsincluding the molding temperature of 300° C. and the mold temperature of80° C. Also, a molded object having an extended residence time wasmanufactured by molding with a molding machine (SH100, made by SumitomoHeavy Industries, Ltd.) and a box-shaped mold having the geometry of 107mm×152 mm×10 mm, with the wall thickness of 2 mm and two pin-gates (1mmφ) under the conditions including the molding temperature of 300° C.,the mold temperature of 80° C. and the cooling time (the molding cycletime; 160 seconds) of 130 seconds. Reflectance and appearance (presenceor absence of silver streak) of each molded object were evaluated. Thereflectance was evaluated based on the Y value determined with an LCMspectrophotometer (MS2020 plus, made by Macbeth Corp.). The appearancewas visually evaluated. The parameter values were determined accordingto the formula: the parameter value=[the blending ratio of titaniumoxide powder (mass %)/the blending ratio of thermoplastic resin (mass%)]×[the total amount of metal cations in the titanium oxide particlesbefore or after water-washing (mass ppm)]. The results are shown inTable 2.

In addition, a corrugated reflecting plate having the geometry of 300mm×240 mm×1 mm was obtained by molding with an injection molding machine(AZ7000, injection pressure; 350 tons, made by Nissei Plastic IndustrialCo., Ltd.) under the conditions including the molding temperature of310° C. and the mold temperature of 95° C.

Further, an extruded sheet having a thickness of 1 mm was obtained byextruding with a 65 mmφ mono-axis extruder furnished with a T-shaped dielip (a width of 60 cm) (SHT65-32DVg, made by Hitachi Zosen Corporation)under the conditions including the cylinder temperature of 260° C., themold temperature of 240° C. and the roll temperature of 120 to 180° C.Further, the sheet was hot-press molded at 190° C., and a corrugatedmolded object having the geometry of 300 mm×240 mm×1 mm was obtained.The obtained corrugated molded object was confirmed to serve as areflecting plate when a light source was placed thereon.

Comparative Example 1

Pellets etc. were manufactured and evaluated similarly to Example 2,except that, instead of the water-washed product of PF-726, thecommercial product of titanium oxide particles, CR-63 (the titaniumoxide amount of 97 mass %) was used as the titanium oxide particles. Theresults are shown in Table 2.

Comparative Example 2

Pellets etc. were manufactured and evaluated similarly to Example 2,except that, instead of the water-washed product of PF-726, thecommercial product of titanium oxide particles, PF-726 beforewater-washing was used as the titanium oxide particles. The results areshown in Table 2.

Comparative Example 3

Pellets etc. were manufactured and evaluated similarly to Example 3,except that, instead of the water-washed product of CR-90, thecommercial product of titanium oxide particles, CR-90 beforewater-washing was used as the titanium oxide particles. The results areshown in Table 2.

Comparative Example 4

Pellets etc. were manufactured and evaluated similarly to Example 4,except that, the commercial product of titanium oxide particles, CR-85before water-washing was used as the titanium oxide particles instead ofthe water-washed product of CR-85. The results are shown in Table 2.

Comparative Example 5

Pellets etc. were manufactured and evaluated similarly to example 8,except that, instead of the water-washed product of PC-3, the commercialproduct of titanium oxide particles, PC-3 before water-washing was usedas the titanium oxide particles. The results are shown in Table 2.

TABLE 2-1 Blending ratio Example 1 Example 2 Example 3 Example 4 Example5 Example 6 Thermoplastic resin PC 84 84 84 84 60 (parts by weight)PC-PDMS 20 60 PMMA PBT Titanium oxide Water-washed 16 16 20 40 particlesproduct of (parts by weight) PF-726 Commercial product of PF-726Water-washed 16 product of CR-90 Commercial product of CR-90Water-washed 16 product of CR-85 Commercial product of CR-85 Commercialproduct of CR-63 Water-washed product of PC-3 Commercial product of PC-3Flame retardant PFR 3 5 5 5 (parts by weight) PTFE Algoflon 0.5 0.5 0.50.5 0.5 0.5 (parts by weight) Organopolysiloxane BY16-161 0.8 0.8 0.80.8 1 2.5 (parts by weight) SH1107 Test result Total amount 1 1 2 2 1 3of metal ions in a pellet (mass ppm) Thermal ⊚ ⊚ ⊚ ⊚ ⊚ ∘ stability inresidence Reflectance 97.5 97.5 98.2 97.8 97.8 97.7 (Y value) Parameter3.8 3.8 9.5 11.4 5.0 13.3 value (mass ppm) Notes: Evaluation ofstability in residence ⊚: Silver streak is absent, and appearance isgood. ∘: Silver streak is almost absent, and appearance is good. x:Silver streak is slightly observed, and appearance is poor. xx: Manypieces of silver streak are observed, and appearance is poor. xxx:Significantly many pieces of silver streak are observed, and appearanceis poor.

TABLE 2-2 Compara- Compara- Compara- Compara- Compara- tive tive tivetive tive Blending ratio Example 7 Example 8 example 1 example 2 example3 example 4 example 5 Thermoplastic resin 65 65 84 84 84 84 65 (parts byweight) PC-PDMS PMMA 25 PBT 25 25 Titanium oxide Water-washed particlesproduct of (parts by weight) PF-726 Commercial 16 product of PF-726Water-washed 10 product of CR-90 Commercial 16 product of CR-90Water-washed product of CR-85 Commercial 16 product of CR-85 Commercial16 product of CR-63 Water-washed 10 product of PC-3 Commercial 10product of PC-3 Flame retardant PFR 5 5 5 5 (parts by weight) PTFEAlgoflon 0.5 0.5 0.5 0.5 0.5 0.5 (parts by weight) OrganopolysiloxaneBY16-161 0.2 0.8 0.8 0.8 0.8 0.2 (parts by weight) SH1107 0.6 Testresult Total amount 1 2 2 4 5 8 3 of metal ions in a pellet (mass ppm)Thermal ∘ ∘ ⊚ x xx xxx x stability in residence Reflectance 97.4 97.595.8 97.5 97.9 98.2 98.2 (Y value) Parameter 5.6 10 7.6 23.6 27.8 40.815 value (mass ppm) Notes: Evaluation of stability in residence ⊚:Silver streak is absent, and appearance is good. ∘: Silver streak isalmost absent, and appearance is good. x: Silver streak is slightlyobserved, and appearance is poor. xx: Many pieces of silver streak areobserved, and appearance is poor. xxx: Significantly many pieces ofsilver streak are observed, and appearance is poor.

INDUSTRIAL APPLICABILITY

A thermoplastic resin composition of the present invention has excellentthermal stability in residence, reflectance and appearance, becausetitanium oxide whose properties are regulated by removal of impurities.Therefore, the thermoplastic resin composition of the present inventioncan be preferably used in the sectors, for example, of office automationequipment, electrical and electronic equipment, etc.

1. A thermoplastic resin composition comprising (A) 40 to 98 mass % of athermoplastic resin; and (B) 60 to 2 mass % of coated titanium oxideparticles, wherein the thermoplastic resin is a polycarbonate-type resinor a blend of a polycarbonate-type resin and another thermoplasticresin; the coated titanium oxide particles comprise titanium oxide whosesurface is coated with a hydrous oxide and/or an oxide of at least onemetal selected from the group consisting of aluminum, silicon,zirconium, tin, cerium, titanium and zinc; the coated titanium oxideparticles contain 80 to less than 97 mass % of titanium oxide; and thecoated titanium oxide particles contain alkali metal cations that can beextracted to water and alkaline-earth metal cations that can beextracted to water in a total amount of 120 mass ppm or lower.
 2. Thethermoplastic resin composition according to claim 1, wherein the metalhydrous oxide and/or the metal oxide as ingredient (B) is silica and/oralumina.
 3. The thermoplastic resin composition according to claim 1,wherein, when the total amount of alkali metal cations andalkaline-earth metal cations that can be extracted to water isdesignated as X (mass ppm), the value of [the blending ratio of titaniumoxide powder (mass %)/the blending ratio of thermoplastic resin (mass%)]×[X (mass ppm)] is 15 mass ppm or less.
 4. A thermoplastic resincomposition, wherein (C) 0.05 to 3 parts by weight of anorganopolysiloxane is blended to 100 parts by weight of thethermoplastic resin composition according to claim
 1. 5. Thethermoplastic resin composition according to claim 1, wherein the totalamount of alkali metal cations and alkaline-earth metal cations that canbe extracted from the thermoplastic resin composition is 3 mass ppm orless based on titanium oxide.
 6. A molded object manufactured by moldingof the thermoplastic resin composition according to claim
 1. 7. Themolded object according to claim 6, wherein the molded object is eitheran extrusion molded object or an injection molded object.
 8. The moldedobject according to claim 7, wherein the injection molded object is areflecting plate.
 9. The molded object according to claim 6, wherein thetotal amount of alkali metal cations and alkaline-earth metal cationsthat can be extracted from the molded object is 3 mass ppm or less basedon titanium oxide.
 10. Coated titanium oxide particles comprisingtitanium oxide whose surface is coated with a hydrous oxide and/or anoxide of at least one metal selected from the group consisting ofaluminum, silicon, zirconium, tin, cerium, titanium and zinc, whereinthe coated titanium oxide particles contain 80 to less than 97 mass % oftitanium oxide; and the coated titanium oxide particles contain alkalimetal cations that can be extracted to water and alkaline-earth metalcations that can be extracted to water in a total amount of 120 mass ppmor lower.
 11. The coated titanium oxide particles according to claim 10,wherein the metal hydrous oxide and/or the metal oxide is silica and/oralumina.
 12. The coated titanium oxide particles according to claim 10,whose surface is further coated with an organopolysiloxane.
 13. Thethermoplastic resin composition according to claim 1, wherein thethermoplastic resin comprises 50 mass % or more of thepolycarbonate-type resin.
 14. The thermoplastic resin compositionaccording to claim 1, wherein the coated titanium oxide particles have aparticle size in a range of from 0.1 to 0.5 μm.
 15. The thermoplasticresin composition according to claim 10, wherein the coated titaniumoxide particles have a particle size in a range of from 0.1 to 0.5 μm.16. The thermoplastic resin composition according to claim 1, whereinthe titanium oxide comprises rutile.
 17. The thermoplastic resincomposition according to claim 10, wherein the titanium oxide comprisesrutile.